Direct Aircraft Velocity Determination by L-Band Moving Target Detector Radar.

The Moving Target Detector MTD radar can be used to measure the phase difference of echoes from aircraft returns. From these measurements one can determine directly the radial component of aircraft velocity. Present practice is to determine velocity indirectly from radar position measurements. Results of measuring phase shift differences and corresponding aircraft velocities using an L-Band MTD radar are presented. Observations were made in a clutter free environment. The standard deviation of phase shift differences made from observations on a B727 airplane at a distance of 100 nmi was generally found to be 5 degrees, corresponding to a standard deviation of velocity component of 1.2 knots. The standard deviation of phase shift observed from six slower moving airplanes indicates the standard deviation of phase is generally 18 degrees or less, corresponding to a standard deviation of velocity component of 4.3 knots or less. Reliability is generally 94 for the B727 airplane and about 90 for the small airplanes, although poorer reliability is observed with tangential flight paths. Direct measurement of velocity can be used to provide increased precision in predicting aircraft motion over the short term 2 minutes.